1. Field of the Invention
The present invention generally relates to a network system having different attributes of terminal equipment devices, such as telephone sets, personal computers, G3 (group 3) facsimile machines and G4 (group 4) facsimile machines. More particularly, the present invention is directed to improvements in a network system having extension lines to which different attributes of terminal equipment devices are coupled.
2. Description of Related Art
Currently, there is a trend in which different attributes of terminal equipment devices other than telephone sets, such as personal computers, G3 facsimile machines and G4 facsimile machines are coupled to extension lines of a network system such as a network control unit (NCU), network terminating equipment or a digital service unit in an ISDN (Integrated Services Digital Network) system. In such a system, an identification number (address) such as a telephone number is provided for each terminal equipment device. For example, when an operator inputs an identification number, only a corresponding terminal equipment device is called. In other words, it is impossible for the calling operator to call a different terminal equipment device or a plurality of terminal equipment devices by the above identification number. This is inconvenient to users. Thus, there is a demand to eliminate the above-mentioned inconvenience be eliminated.
A network system has been proposed in which an identification number such as a telephone number identifies a group of terminal equipment devices and one of the grouped terminal equipment devices having the same attribute as the calling terminal equipment device is called.
Referring to FIG. 1, there is illustrated a conventional network system in conformity with an ISDN user/network interface recommended by the CCITT. A plurality of extension lines 30, 70 and 80 are coupled to a network 100 such as a line terminating equipment. The frequency range on each of the extension lines 30, 70 and 80 is divided into two information channels (B channels) and a signal channel (a D channel). Each B channel transfers communication data such as voice data or facsimile data. The D channel transfers either call control information such as dial information which may be necessary for each terminal equipment device to be coupled to the network 100 or answer information which is sent to each terminal equipment device.
In FIG. 1, a G4 facsimile machine 3 is connected to the extension line 30. A digital telephone set 7-1, a personal computer 7-2 and a G4 facsimile machine 7-3 are connected to the extension line 70. A digital telephone set 8-1, a personal computer 8-2 and a G4 facsimile machine 8-3 are connected to the extension line 80. An identification number or telephone number is determined for each of the extension lines 30, 70 and 80.
It is now assumed that a telephone number representative of the extension line 70 (pilot, agent or representative telephone number) is sent to the network 100 through the G4 facsimile line 3 which is currently a calling terminal equipment device. The network 100 changes the extension line 70 from an idle state to a called state in which call setup information and attribute information about the G4 facsimile machine 3 are sent to the extension line 70. Assuming that the attribute information about the G4 facsimile machine 3 is "0003", each of the terminal equipment devices 7-1, 7-2 and 7-3 connected to the extension line receive the call setup information and the attribute information, and determines whether its own attribute coincides with the attribute of the G4 facsimile machine 3. When a terminal equipment device determines that its own attribute coincides with the attribute of the G4 facsimile machine 3, the terminal equipment device having the same attribute responds to the call setup.
The conventional network system shown in FIG. 1 is disadvantaged by the fact that it is not possible to call each terminal equipment device by a plurality of pilot (representative) telephone numbers. For example, the G4 facsimile machine 8-3 can be called by only a pilot telephone number indicative of the extension line 80 and thus cannot be called by another pilot telephone number such as a pilot telephone number indicating the extension line 70. Also, when the G4 facsimile machines 7-3 and 8-3 are used in common by two sections of a company which are separately assigned the extension lines 70 and 80, it is desired that the G4 facsimile machine 7-3 can be called by not only a telephone number indicative of the extension line 70 but also a telephone number indicative of the extension line 80.